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1.
Groundnut leaves, naturally infected in the field with Cercospora arachidicola or artificially infected in the greenhouse with C. arachidicola or Puccinia arachidis , accumulated isoflavonoid phytoalexins. Major compounds included medicarpin, formononetin, demethylmedicarpin, three isoflavanones and the isoflavone, daidzein. In both greenhouse and field experiments cv. Egret was less susceptible than cv. P84/5/244 to both pathogens, and accumulated phytoalexin (medicarpin) concentrations which were up to three times greater. Higher concentrations and greater variation of phytoalexins were detected when both cultivars were infected with C. arachidicola than when they were infected with P. arachidis.  相似文献   

2.
The effect of temperature on the latent periods of rust, late leaf spot and early leaf spot diseases of groundnut caused by Puccinia arachidis, Phaeoisariopsis personata and Cercospora arachidicola , respectively, was studied. The latent periods (LP) of rust, late leaf spot and early leaf spot ranged from 12–49 days, 13–38 days and 13–39 days, respectively, between 12°C and 33°C An equation relating the rate of pathogen development (1/LP) to temperature was fitted using daily mean temperatures to provide three cardinal temperatures: the minimum (Tmln), optimum (Topl), and maximum (Tmax), Tmln was about 12°C for rust and about 10°C for the two leaf-spot diseases. Topt, for all three diseases was close to 25°C. Tmax was 31°C for early leaf spot, and extrapolated values for late leaf spot and rust were about 35 and 40°C, respectively.
For P. personata , a temperature response curve was fitted using data only from controlled environment experiments. This curve was used to simulate latent periods from both mean daily and mean hourly temperatures in the field. There was substantially better agreement between observed and simulated latent period with hourly temperatures, provided the developmental rate of the pathogen was determined at a constant temperature.  相似文献   

3.
Grey leaf spot is an important maize foliar disease caused by the fungal pathogens Cercospora zeae-maydis and Cercospora zeina. Although methods exist to detect these Cercospora species in maize, current techniques do not allow quantification of the fungi in planta. We developed a real-time SYBR® Green PCR assay for quantification of grey leaf spot disease in maize based on the amplification of a fragment of a cytochrome P450 reductase (cpr1) gene. In planta fungal DNA content was normalised to a maize glutathione S-transferase III gene (gst3) to yield values of ng Cercospora DNA/mg maize DNA. The assay was specific to the two Cercospora spp., and we observed no amplification of the cpr1 fragment in non-target maize leaf pathogens or saprophytes. The assay was employed to quantify C. zeina in glasshouse inoculated maize plants and grey leaf spot infected field plants of resistant and susceptible maize lines. In both instances, C. zeina DNA content correlated with symptomatic leaf lesion area, and the susceptible maize line contained significantly more C. zeina DNA than the resistant line. Sequence differences between the C. zeina and C. zeae-maydis cpr1 amplicons enabled us to perform melt curve analyses to identify the Cercospora species causing grey leaf spot at a particular location. This assay has application in the early detection and quantification of Cercospora spp., both of which are important tools in grey leaf spot disease management and maize breeding programmes.  相似文献   

4.
ABSTRACT The effects of temperature and duration of wetness (relative humidity >/=95%) on infection of three peanut cultivars by Cercospora arachidicola were determined under controlled conditions. Plants of the Spanish cv. Spanco and the runner cvs. Florunner and Okrun were exposed to constant temperatures of 18 to 30 degrees C during 12-h periods of wetness each day that totaled 12 to 84 h following inoculation of leaves with conidia. Severity of disease, measured by either lesion density (number per leaf) or lesion size (diameter), was greatest for 'Spanco', intermediate for 'Florunner', and lowest for 'Okrun' in each of two experiments. Lesion density was evaluated further because it was an indicator of both the occurrence and degree of infection. Nonlinear regression analysis was employed to evaluate the combined effects of temperature (T) and wetness duration (W) on lesion density (Y). In the regression model, the Weibull function characterized the monotonic increase of Y with respect to W, while a hyperbolic function characterized the unimodal response of Y with respect to T. Parameters for the intrinsic rate of change with respect to W (b), the intrinsic rate of change with respect to T (f), the optimal value of T (g), and the upper limit (e) when T is optimum (T = g) were estimated for each cultivar and experiment. The effect of cultivar was characterized primarily by differences in the upper limit parameter e. In each experiment, e was greatest for 'Spanco', intermediate for 'Florunner', and least for 'Okrun'. The effect of cultivar on b followed a pattern similar to that for e in experiment 1, but not in experiment 2. Differences among cultivars for estimates of f and g were small and inconsistent. Estimates for g were precise for each cultivar and experiment and fell within the range of 22.3 to 23.2 degrees C. Cultivar responses to T and W were further evaluated using data pooled over the two experiments. Parameter e was estimated for each cultivar, but common values of b, f, and g were estimated. At e = 22.8 degrees C, lesion density approached an upper limit of 96, 17, and 6 lesions per leaf for the cvs. Spanco, Florunner, and Okrun, respectively. These fitted values approximated the observed values of 86, 25, and 9 lesions per leaf for the respective cultivars. Cultivars varied in their response to W at a given T. At 22.8 degrees C, one lesion per leaf was expected following 26, 30, and 36 h of wetness for 'Spanco', 'Florunner', and 'Okrun', respectively. If temperature was increased to 28 degrees C, one lesion per leaf was expected following 36, 44, and 54 h of wetness for the respective cultivars.  相似文献   

5.
ABSTRACT The genus Cercospora is one of the largest genera of hyphomycetes. Cercospora apii sensu lato is the oldest name for a large complex of morphologically indistinguishable Cercospora spp. occurring on a wide host range. There are currently 659 recognized Cercospora spp., and names of another 281 morphologically identical species are included in the synonymy of C. apii sensu lato. Two of the species that belong to the C. apii complex, C. apii and C. beticola, cause Cercospora leaf spot on Apium graveolens (celery) and Beta vulgaris (sugar beet), respectively. In the present study, multilocus sequence data, amplified fragment length polymorphism analysis, and cultural characteristics were used as additional features to characterize morphologically similar Cercospora strains occurring on celery and sugar beet. From the data obtained, it is shown that C. apii and C. beticola, although morphologically similar and able to cross-infect each others' hosts, are distinct functional species that should be retained as separate entities. Furthermore, a third, as yet undescribed species of Cercospora was detected in celery fields in Korea and Venezuela, suggesting that additional undescribed species also may be found to cause Cercospora leaf spot on celery. A polymerase chain reactionbased diagnostic protocol distinguishes all three Cercospora spp.  相似文献   

6.
ABSTRACT Epidemics of early leaf spot of peanut (Arachis hypogaea), caused by Cercospora arachidicola, are less severe in strip-tilled than conventionally tilled fields. Experiments were carried out to characterize the effect of strip tillage on early leaf spot epidemics and identify the primary target of suppression using a comparative epidemiology approach. Leaf spot intensity was assessed weekly as percent incidence or with the Florida 1-to-10 severity scale in peanut plots that were conventionally or strip tilled. The logistic model, fit to disease progress data, was used to estimate initial disease (y(0)) and epidemic rate (r) parameters. Environmental variables, inoculum abundance, and field host resistance were assessed independently. For experiments combined, estimated y(0) was less in strip-tilled than conventionally tilled plots, and r was comparable. The epidemic was delayed in strip-tilled plots by an average of 5.7 and 11.7 days based on incidence and severity, respectively. Tillage did not consistently affect mean canopy temperature, relative humidity, or frequency of environmental records favorable for infection or spore dispersal. Host response to infection was not affected by tillage, but infections were detected earlier and at higher frequencies with noninoculated detached leaves from conventionally tilled plots. These data suggest that strip tillage delays early leaf spot epidemics due to fewer initial infections; most likely a consequence of less inoculum being dispersed to peanut leaves from overwintering stroma in the soil.  相似文献   

7.
After a cell wall protein fraction (CWP) of Pythium oligandrum was sprayed on sugar beet leaves, we screened leaves for induced expression of defence-related genes and for resistance against Cercospora leaf spot. In a western blot analysis, the CWP was primarily retained on the surface of leaves without degradation for at least 48 h after spraying. In northern blot analyses, four defence-related genes (β-1, 3-glucanase, acidic class III chitinase, 5-enol-pyruvylshikimate-phosphate synthase and oxalate oxidase-like germin) were expressed more rapidly in CWP-treated leaves compared to control leaves treated with distilled water (DW). When CWP was applied to a suspension of cultured cells of sugar beet, an oxidative burst was observed that did not occur after the DW treatment. In growth chamber trials after inoculation with Cercospora beticola, the severity of Cercospora leaf spot was significantly reduced in CWP-treated plants compared to the DW-treated controls. In a field experiment, CWP treatment was also effective against the disease. CWP did not reduce growth rate of the pathogen in plate tests. The results together suggest that the CWP from P. oligandrum can be retained on the leaf surface and induce expression of disease resistance genes, thereby reducing Cercospora leaf spot on sugar beet.  相似文献   

8.
玉米三种叶斑病混发时的流行过程及产量损失研究   总被引：1，自引：0，他引：1  
 通过2年的田间小区人工接种试验,观察比较了玉米大斑病、弯孢叶斑病和灰斑病单独及混合发生时的流行过程及对玉米产量损失的影响。结果表明,在病害混发初期,病害间无明显的负相关性,随着病情的发展,病害间的负相关性逐渐增大并达到显著水平,说明病害间有明显的抑制作用。病害混发时造成产量损失并不完全等于各病害单独造成损失之和,其中大斑病和弯孢叶斑病、弯孢叶斑病和灰斑病混合发生所造成的损失约为各病害单独造成损失之和的76%～88%,大斑病和灰斑病混合发生所造成的损失可近似看作两种病害各自引起产量损失之和,3种病害同时发生时最终损失率约为各自造成损失之和的67%～72%。  相似文献   

9.
Field studies at Bangalore, India, demonstrated that benfiuralin, fluchloralin and profluralin were effective for the selective control of many weed species in field experiments with peanuts (Arachis hypogaea L.‘BH-8-18′). Trifluralin and dinitramine were effective against many weed species but reduced crop stand by about 10%. These two herbicides also reduced the incidence of leaf spot disease (Cercospora arachidicola) and peanut pod yields were similar to clean weeded treatments. Bentazon was ineffective on most weed species and metribuzin was lethal to the crop. Alachlor, nitrofen and chloramben were only partially effective and would require supplemental hand weeding or mechanical tillage to obtain satisfactory weed control.  相似文献   

10.
Grey leaf spot disease of maize (Cercospora zeaemaydis) has seriously decreased grain yields in the province of KwaZulu-Natal, South Africa, and has spread to infect maize in neighbouring provinces. No commercial hybrids, resistant to the disease have so far been identified, and fungicides have been shown to reduce disease severity. The response of sixty-four commercial hybrids to grey leaf spot under fungicide treatment were studied over two seasons. Overall, fungicides reduced disease severity and linear regression of gain in yield against disease severity enables the identification of hybrids with optimum responses to fungicides. Under low disease levels hybrids responded less to fungicides than under high disease levels. The most susceptible hybrids had the highest responses in control of leaf-blighting and gain in yield. Hybrids with lower-than-predicted leaf-blighting also had lower-than-predicted yield responses, indicating these to be less susceptible to grey leaf spot. These less susceptible hybrids are likely to require fewer fungicide treatments than more susceptible hybrids and are at lesser risk of serious yield losses.Abbreviations GLS grey leaf spot - AUDPC area under disease progress curve  相似文献   

11.
ABSTRACT Gray leaf spot, caused by the fungus Cercospora zeae-maydis, causes considerable yield losses in hybrid maize grown in the north-central United States and elsewhere. Nonchemical management tactics have not adequately prevented these losses. The probability of profitably using fungicide application as a management tool for gray leaf spot was evaluated in 10 field experiments under conditions of natural inoculum in Iowa. Gray leaf spot severity in untreated control plots ranged from 2.6 to 72.8% for the ear leaf and from 3.0 to 7.7 (1 to 9 scale) for whole-plot ratings. In each experiment, fungicide applications with propiconazole or mancozeb significantly reduced gray leaf spot severity. Fungicide treatment significantly (P 相似文献   

12.
Abstract

Cercospora leaf spot, caused by Cercospora canescens and powdery mildew, caused by Erysiphe polygoni are two of the most important fungal diseases of mungbeans. Nearly 4000 accessions of the global mungbean collection at the Asian Vegetable Research and Development Center were screened for resistance to these two pathogens. Less than 4% and 12% of the accessions showed resistance to Cercospora leaf spot and powdery mildew, respectively. The level of resistance to Cercospora leaf spot varied and highly resistant lines were not found. A few lines were rated highly resistant to powdery mildew over several years but others were rated moderately resistant or susceptible in other years.  相似文献   

13.
Twelve selected cowpea cultivars were screened for resistance to Cercospora leaf spot (CLS) disease caused by Pseudocercospora cruenta and Cercospora apii s. lat. under artificial epiphytotic conditions in a replicated field trial, with the objective of developing a quantitative measure of disease resistance. CLS incidence, leaf spotting score, lesion density, lesion size, proportion of nodes infected, diseased leaf area, conidia number mg−1 and fascicle density were assessed in 12 cowpea genotypes at crop maturity. Proportion of nodes infected and leaf spotting score were best able to quantitatively differentiate between the levels of resistance, and allow the exploitation of quantitative resistance to the disease. Both lesion density and lesion size were important in determining the final leaf spotting score but the former was epidemiologically more important than the latter, indicated by its correlation to most of the CLS symptom measures. There was differential resistance to the P. cruenta and C. apii s. lat. among the cowpea varieties screened. Among the cowpea lines screened, resistance to P. cruenta was more common than resistance to C. apii s. lat. Nevertheless, P. cruenta was considered the more aggressive and epidemiologically more important than C. apii s. lat. on the varieties tested evidenced by the strong correlation of P. cruenta incidence with acropetal spread of CLS, intensity of leaf spotting, conidia number mg−1 and fascicle density. The highly susceptible varieties namely VRB7, Los Banos Bush Sitao no.1 and CB27 were susceptible to both Cercospora pathogens. The cowpea variety VRB-10 was completely resistant to both pathogens and is a useful source of resistance in CLS breeding programmes.  相似文献   

14.
Phytoparasitica - Cercospora leaf spot, an important disease in coffee caused by the fungus Cercospora coffeicola, can appear as two distinct symptoms on leaves, which are ‘brown eye...  相似文献   

15.
ABSTRACT Genetic variability and population structure of Cercospora sorghi from wild and cultivated sorghum were investigated to gain insight into their potential impact on epidemics of gray leaf spot of sorghum in Africa. Population structure was examined using data derived from amplified fragment length polymorphism (AFLP) of C. sorghi by Nei's test for population differentiation, G(ST), and analysis of molecular variation (AMOVA). Two ecological populations of C. sorghi in Uganda were devoid of population structure (G(ST) = 0.03, small ef, CyrillicF(ST) = 0.01, P = 0.291). AMOVA revealed that genetic variability was due mainly to variations within (99%) rather than between (0.35%) populations, and Nei's genetic distance between the two populations was 0.014. Phenetic analysis based on AFLP data and polymerase chain reaction-restriction fragment length polymorphism analyses of the internal transcribed spacer regions of rDNA and mitochondrial small subunit rDNA separated Cercospora cereal pathogens from dicot pathogens but did not differentiate among C. sorghi isolates from wild and cultivated sorghum. Our results indicate that Ugandan populations of C. sorghi compose one epidemiological unit and suggest that wild sorghum, while not affecting genetic variability of the pathogen population, provides an alternative host for generating additional inoculum.  相似文献   

16.
Integrated Management Practices for the Control of Maize Grey Leaf Spot   总被引：1，自引：0，他引：1  
Grey leaf spot of maize, (Zea maydis L.) (Cercospora zeae-maydis) Tehon and Daniels, is one of the most destructive leaf diseases of maize. The distribution and severity of grey leaf spot has increased over the past 10 to 15 years. The United States and South Africa are main areas where research on the disease has been concentrated. The research results have provided valuable and significant insight into pathogen epidemiology and allowed an integrated management system to be developed. However, management options are a result of the agricultural system under which maize is produced. The pathogen survives only on maize, so crop rotation and stubble management are major factors in disease management, but resistant hybrids offer the best option for economic control. Many other factors, such as soil fertility, plant density, irrigation and chemical control, can significantly influence a grey leaf spot epidemic, although a single management practice will not control the pathogen effectively.  相似文献   

17.
Cercospora beticola is the main causal agent of cercospora leaf spot on sugar beet and has a large negative impact on the yield and quality of sugar beet production worldwide. Previous studies have shown that both mating type idiomorphs of C. beticola are present in natural populations, suggesting that C. beticola is heterothallic and may be reproducing sexually. Cercospora beticola isolates are diverse in the morphology of their conidia, onset of disease symptoms and fungicide resistance. To find the source of this diversity and to determine if sexual reproduction occurs in this fungus, C. beticola populations were collected from Western Europe, Iran and New Zealand. The mating types of these isolates were determined and AFLP analyses were used to study the genetic diversity in these populations. The mating type ratios did not deviate significantly from a 1:1 ratio in most of the populations and AFLP analyses showed high levels of genetic variation within and between the populations, with 86·4% of the isolates having unique genotypes. All populations were in significant linkage disequilibrium but levels of disequilibrium were low, and loci from only one primer pair were in significant gametic equilibrium in populations from the Netherlands and Italy. From these results there is the possibility that C. beticola reproduces sexually. High levels of gene flow among the samples from Europe demonstrated a single panmictic European population. This study confirms C. beticola to be a genetically highly diverse species, supporting the assumption that some populations are reproducing sexually.  相似文献   

18.
Weeds and diseases can reduce peanut (Arachis hypogaea L.) yield or increase cost of production to maintain acceptable yield. While herbicides and fungicides have limited availability in many areas of Ghana and currently are too expensive for resource-poor farmers, control by these pesticides can have a major positive impact on peanut yield. Field experiments were conducted during the rainy seasons of 2009 and 2010 in northern Ghana to determine the effects of herbicide and hand weeding in combination with fungicides on pest management and peanut yield. Peanut pod yield was often more highly correlated with disease severity and canopy defoliation resulting from early leaf spot (caused by Cercospora arachidicola Hori) and late leaf spot (caused by Cercosporidium personatum (Berk. & M.A. Curtis) Deighton) than weed biomass. In some instances, less disease and canopy defoliation were observed when weeds were not controlled effectively compared with increased weed management through hand weeding or herbicide. Two hand weedings or applying pendimethalin preemergence with one hand weeding in combination with 4 applications of triadimefon and chlorothalonil resulted in the lowest weed density and canopy defoliation and often resulted in the highest peanut yield.  相似文献   

19.
ABSTRACT In microplot experiments in 1998-99 and 1999-2000, the start of light leaf spot epidemics could be predicted from weather data, using empirical equations for Pyrenopeziza brassicae apothecial (ascospore) development, ascospore infection criteria, and the latent period of P. brassicae. The dates when P. brassicae sporulation was first observed fitted predictions and initial spread of light leaf spot from an inoculum source was mostly in the prevailing wind direction, with differences between the two growing seasons attributable to differences in wind patterns. Subsequent secondary spread of disease could be predicted using temperature and rainfall data, and observations fitted predicted dates. In both 1998-99 and 1999-2000, initial spatial patterns of observed disease in January were random, because data were not significantly different from a binomial distribution (P = 0.18). Analysis of spatial data from samples in February and March indicated aggregation, because data fit was significantly different from a binomial distribution (P 相似文献   

20.
Cercospora leaf spot, caused by the fungus Cercospora beticola, is a major fungal sugar beet disease worldwide and the cause of significant yield losses. The disease is most successfully countered by the introduction of genetic tolerance into elite sugar beet hybrids. To this end, breeding programmes require high quality biological assays allowing discrimination of minor differences between plants within a segregating population. This study describes the successful implementation of image analysis software in the bioassays for quantification of necrotic lesions at different stages of C. beticola infection, allowing selection on minor phenotypic differences during the sugar beet breeding process for C. beticola resistance. In addition, a real‐time PCR assay was developed for the quantification of C. beticola pathogen biomass in infected beet canopy. The use of both techniques, even in an early stage of infection, fine‐tunes current bioassays, allowing more accurate and efficient selection of resistant breeding material.  相似文献   

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